This invention relates to an agitating mill having a cylindrical grinding container, whose grinding space is partially filled with grinding media, and a rotatably drivable mixer mounted concentrically therein. The present invention relates more particularly to such an agitating mill having a mixer provided with hollow mixing shaft and mixing bars mounted extending approximately radially outward therefrom, the grinding container being provided with a grinding-stock inlet and a ground-stock outlet.
An agitating mill of this type is known from Swiss Pat. No. 132,086, wherein the mixing bars serve to impart pulsed movements to the grinding media contained in the grinding container. The continuous acceleration and braking of the grinding media causes the particles of grinding stock, in the form of a suspension or a dispersion, to be ground between the grinding media. The mixing shaft, made hollow in the known agitating mill, is used to add the liquid grinding stock. The crushing and dispersion effect is not optimal in this known agitating mill, i.e. especially during continuous operation, the insufficiently crushed particles of grinding stock must be separated by sedimentation and recycled into the grinding space.
It is already known from German Pat. No. 1,214,516 to provide in the grinding container, a closed cylinder extending over the entire length of the container and to provide mixing bars in the annular space formed by the outside wall of the cylinder and the inside wall of the grinding container. The hollow cylinder is coolable. The purpose of this design is to achieve a homogeneous ground product by means of a maximally homogeneous movement throughout the entire system of the grinding stock and grinding media. In the narrow annular space, the grinding media should be able to move without significant differences in velocity. Starting agitating mills of this known type has proven to be especially difficult.
German Auslegeschrift No. 1,211,905 discloses an agitating mill in which mixing elements in the form of solid mixing discs are provided on the mixing shaft, wherein the shape of the outside edges of the mixing discs is not circular and differs from a circular cross section. An agitating mill of this type is well suited for the preparation of solid dispersions in liquids with approximately Newtonian behavior; this agitating mill is less suitable for liquids with considerably different behaviors. Moreover, a relatively poor cellular flow is produced in this known agitating mill in the areas between adjacent the mixing discs.